It is a known feature of acoustic reproducing equipment to use a signal light as an operation indicator which, for example, can be seen by a speaker or the like. It is also a known feature in the case of film or television cameras to utilize a light on the camera which is continuously illuminated when the camera is photographing. For this purpose, for example, a switch in the circuit of the signal light is closed by the trigger of the film camera. The arrangement of a signal light which indicates that the camera is in operation offers an actor the advantage that he is always aware that he is being filmed but it also has the disadvantage in that he must always watch the camera in order to see the signal light. When scenery is filmed, however, the reaction of the actor to the camera to observe this signal can be extremely disturbing. Furthermore, in strong sunlight, the signal flash is often difficult to see since its light emission, especially in amateur cameras is low in order not to overload the power supply of the camera.
In the case of film cameras, the use of acoustic signal devices which inform the cameraman as to the possible operational parameters of the camera is known. Thus, it has already been proposed to periodically send radiating sound signals to the cameraman during operation of the camera in order to determine the scene length. However, such a device cannot be used in sound-film cameras for synchronized taking of picture and sound information since they disturb the sound recording.